The present invention relates to an ink jet recording head for ejecting ink droplets onto a recording medium to form an image, and in particularly to the structure of a spacer for forming a channel for a pressure generating chamber and a reservoir.
As is disclosed in, for example, Japanese Patent Publication No. 9-226112A, an ink jet recording head comprises: arrays of pressure generating chambers; a channel unit that is formed by laminating a spacer, in which a reservoir is formed that communicates with the pressure generating chambers via ink supply ports, a nozzle plate, in which nozzle orifices are formed to communicate with the pressure generating chambers, and an elastic plate for sealing the pressure generating chambers and the reservoir; a pressure generating member for deforming the elastic plate in an area opposite the pressure generating chamber; and a head holder, including an ink guide passage along which ink is introduced into the reservoir, for fixing the channel unit to the pressure generating member.
In such an ink jet recording head, ink from an external ink container is supplied to the reservoir, and is transferred to the pressure generating chambers via the ink supply ports. Pressure is applied to the ink in the pressure generating chambers by the pressurization means and is ejected as ink droplets at the nozzle orifices.
When an empty ink container, normally, an empty ink cartridge, is replaced by a new one, air bubbles enter into the reservoir and block the ink supply ports, so that ink droplets can not be ejected. Thus, to discharge air bubbles from the reservoir, the nozzle plate is closed with a cap member and ink is forcibly discharged from the reservoir by the application of a negative pressure produced by a suction pump.
However, since the negative pressure produced by the suction pump causes a flow of ink in the reservoir, pressure gradient occurs from the center portion of the reservoir to the end portion thereof. Then, some of the air bubbles that entered the reservoir are prevented from flowing across the wall of the reservoir into the ink supply ports that are located in the center portion of the reservoir, and instead, are moved along the side wall of the reservoir to the end portion and are retained there.
Since at the end portion of the reservoir the amount of ink flow per unit area is smaller than at the center portion, the force available for the discharge of air bubbles is so small that the air bubbles retained at the end portion of the reservoir are difficult to remove.